Cleaning method and vapor phase growth device

Abstract

Provided are a cleaning method and a vapor phase growth device that enable easy removal of deposits including carbon adhering to the inner wall of a flow channel. This cleaning method for deposits (24) in a vapor phase growth device (100) in which an electric furnace (10) is used to heat a reaction tube (1) includes passing oxygen gas through a flow channel disposed in the reaction tube (1) to clean away the deposits (24) containing carbon adhering to the inner wall of the flow channel.

Description

Cleaning method and vapor phase growth apparatus

[0001] The present invention relates to a cleaning method and a vapor phase growth apparatus.

[0002] β-Ga ２ O ３ has a large bandgap energy (~4.5 eV) and is expected to have a high breakdown field strength (>7 MV / cm), making it a promising material for next-generation power devices. The fabrication of vertical devices requires the growth of a thick n-type drift layer with controlled conductivity, and halide vapor phase epitaxy (HVPE) has been used to date. Meanwhile, metalorganic vapor phase epitaxy (MOVPE) allows for highly precise film thickness control and alloy growth.

[0003] Patent Document 1 describes a vapor phase growth method for III-V group compound semiconductor films. ２ O ３ It has been reported that epitaxial films have been formed.

[0004] Japanese Unexamined Patent Publication No. 2-252699

[0005] F. Alema, B. Hertog, A. Osinsky, P. Mukhopadhyay, M. Toporkov, and W. V. Schoenfeld, Journal of Crystal Growth Vol. 475, pp. 77-82 (2017).

[0006] Conventionally, to remove deposits, the flow channel has been removed from the MOVPE apparatus and immersed in a liquid such as potassium hydroxide or hydrofluoric acid for wet cleaning. Alternatively, dry cleaning has been performed using a chlorine-based gas. In the MOVPE method described in Patent Document 1, the Group III organic metal source decomposes into metal and carbon inside the source gas supply pipe, which can result in carbon-containing deposits adhering to the inner wall of the source gas supply pipe.

[0007] The present invention has been made in view of the above circumstances, and provides a cleaning method and a vapor phase growth apparatus that can easily remove carbon-containing deposits adhering to the inner walls of a flow channel.

[0008] In order to solve the above problems, the present invention employs the following configurations. [1] A method for cleaning deposits in a vapor phase growth apparatus using an electric furnace to heat a reaction tube, comprising flowing oxygen gas through a flow channel disposed within the reaction tube to clean carbon-containing deposits adhering to the inner wall of the flow channel. [2] A vapor phase growth apparatus using an electric furnace to heat a reaction tube, comprising: a function for growing a compound semiconductor film on a substrate by flowing an organic metal and a reactive gas through a flow channel disposed within the reaction tube; and a function for cleaning carbon-containing deposits adhering to the inner wall of the flow channel by flowing oxygen gas through the flow channel. [3] The vapor phase growth apparatus according to [2], wherein the electric furnace heats the vapor phase growth apparatus so that the temperature at a position where the substrate is placed is higher than the temperature at a position where the organic metal and the reactive gas meet when growing the compound semiconductor film on the substrate, and the electric furnace heats the vapor phase growth apparatus so that the temperature at the meet point is higher than the temperature at the position where the substrate is placed when cleaning the carbon-containing deposits.

[0009] According to the present invention, carbonaceous deposits adhering to the inner walls of the flow channel can be easily removed.

[0010] 1A and 1B are vertical and horizontal cross-sectional views of a vapor phase growth apparatus according to an embodiment of the present invention;

[0011] 1 and 2 are cross-sectional views illustrating a vapor phase growth apparatus according to an embodiment, in which Fig. 1 shows a cross section along a plane perpendicular to a substrate (a vertical cross section), and Fig. 2 shows a cross section along a plane parallel to the substrate (a horizontal cross section).

[0012] The vapor phase growth apparatus 100 according to the embodiment uses an electric furnace 10 to heat a reaction tube 1. For example, the vapor phase growth apparatus 100 can grow a compound semiconductor film (not shown) on a substrate 2 using a MOVPE method. A specific example of the vapor phase growth method is a hot wall MOVPE method.

[0013] The vapor phase growth apparatus 100 includes a reaction tube 1 in which a substrate 2 is placed, and an electric furnace 10 for heating the reaction tube 1. The reaction tube 1 corresponds to a reactor. The material of the reaction tube 1 is not particularly limited, but may be, for example, SiO ２ , SUS, etc. The electric furnace 10 corresponds to a heating device used to heat the reaction tube 1, and in the illustrated example, a zone heater is used. The substrate 2 is held by a hanging-type substrate holder 3.

[0014] In the illustrated example, an upstream flow channel 20, an intermediate flow channel 26, and a downstream flow channel 29 are formed within the reaction tube 1. The upstream flow channel 20 corresponds to a source gas flow path that guides a plurality of source gases to a junction position A. The intermediate flow channel 26 and the downstream flow channel 29 are flow paths that guide the mixed gas from the junction position A to the surface of the substrate 2 and then discharge it, and correspond to a mixed gas flow path.

[0015] In the illustrated example, the upstream flow channel 20 has three flow paths formed therein, from top to bottom: a top channel 21, a middle channel 22, and a bottom channel 23. The middle channel 22 serves as a source gas flow path for supplying a first source gas G1 to the substrate 2, and the top channel 21 and the bottom channel 23 serve as source gas flow paths for supplying a second source gas G2 to the substrate 2.

[0016] 1 and 2, the vertical cross section of the illustrated upstream flow channel 20 decreases in diameter from upstream to downstream, and the horizontal cross section increases in diameter from upstream to downstream. The downstream end of the upstream flow channel 20 has a flat shape that expands horizontally. The first source gas G1 flows out from the vertical center, and the second source gas G2 flows out from above and below.

[0017] The intermediate flow channel 26 is connected to the downstream side of the upstream flow channel 20. This connection point, i.e., the upstream end of the intermediate flow channel 26, corresponds to a confluence position A where multiple source gases converge. At the confluence position A, the first source gas G1 flowing out of the middle channel 22 and the second source gas G2 flowing out of the top channel 21 and the bottom channel 23 converge, and the resulting mixed gas flows through the intermediate flow channel 26.

[0018] A hanging-type substrate holder 3 is fitted into an upper opening 27 formed in the upper pipe wall of the intermediate flow channel 26. The hanging-type substrate holder 3 has a plurality of claws for supporting the substrate 2 on its underside facing the interior of the intermediate flow channel 26. By placing the substrate 2 on the hanging-type substrate holder 3, the lower surface of the substrate 2 is exposed to the mixed gas in the intermediate flow channel 26. By using a so-called face-down type in which the lower surface of the substrate 2 is exposed to the mixed gas, it is easy to avoid unexpected particle adhesion, etc.

[0019] The downstream flow channel 29 is connected to the downstream side of the intermediate flow channel 26. The mixed gas that has passed through the intermediate flow channel 26 is discharged from the downstream side of the downstream flow channel 29 to the outside of the reaction tube 1. In the reaction tube 1, a gas such as nitrogen may be circulated in the spaces outside the upstream flow channel 20, the intermediate flow channel 26, and the downstream flow channel 29.

[0020] A source gas supply pipe is connected to the upstream side of the upstream flow channel 20. Specifically, a first source gas supply pipe 31 is connected to the middle channel 22, and a first source gas G1 is supplied to the middle channel 22. A second source gas supply pipe 32a is connected to the top channel 21, and a second source gas G2 is supplied to the top channel 21. A second source gas supply pipe 32b is connected to the bottom channel 23, and a second source gas G2 is supplied to the bottom channel 23.

[0021] The electric furnace 10 is provided in a ring shape along the outer wall of the reaction tube 1. The illustrated zone heater comprises an upstream heater 11, an intermediate heater 12, and a downstream heater 13, and the temperatures of these heaters can be set individually.

[0022] The upstream heater 11 is disposed within the outer wall of the reaction tube 1 around the upstream portion of the intermediate flow channel 26 so as to heat the vicinity of the point where the first source gas G1 and the second source gas G2 join. The intermediate heater 12 is disposed within the outer wall of the reaction tube 1 around the portion surrounding the top surface opening 27 so as to heat the portion where the substrate 2 is placed. The downstream heater 13 is disposed within the outer wall of the reaction tube 1 around the portion surrounding the downstream side of the top surface opening 27 so as to heat the downstream side of the top surface opening 27 and the downstream flow channel 29.

[0023] To manufacture a compound semiconductor film using the vapor phase growth apparatus 100, the substrate 2 is suspended by the hanging-type substrate holder 3, and a mixed gas is brought into contact with the lower surface of the substrate 2 under predetermined heating conditions. Although not shown, the vapor phase growth apparatus 100 may be of a so-called face-up type in which the upper surface of the substrate 2 is exposed to the mixed gas. By forming a lower opening in the lower wall of the intermediate flow channel 26 and fitting an upper-type substrate holder into it, the substrate 2 can be arranged in a face-up position.

[0024] The compound semiconductor film formed on the substrate 2 is β-Ga ２ O ３ Examples of suitable metal oxide films include metal oxide films such as those described above. The mixed gas supplied to the vapor phase growth apparatus 100 contains a vaporized metal organic compound and a reactive gas in a carrier gas. Examples of the carrier gas include argon gas and helium gas. By flowing the metal organic compound and the reactive gas through the flow channel, a compound semiconductor film can be grown on the substrate 2.

[0025] Examples of organic metals include, for example, organic aluminum, organic gallium, and organic indium when forming a compound semiconductor of a group III element. For example, sources of group III elements include trimethylaluminum (TMAl), trimethylgallium (TMGa), and trimethylindium (TMIn). Depending on the type of compound semiconductor film, organic metals other than group III elements can also be used.

[0026] When a metal oxide film is formed from an organic metal, oxygen gas is used as the reactive gas. When a metal compound other than a metal oxide is formed from an organic metal, an appropriate reactive gas can be used depending on the type of metal compound. ２ O ３ When silicon is doped as an n-type impurity into the semiconductor layer, monosilane, tetramethylsilane, tetraethylsilane, etc. may be used as a silicon dopant. The dopant is not limited to silicon, and an appropriate dopant gas may be used depending on the type of metal compound.

[0027] When an organic metal and a reactive gas are flowed through the flow channel, the organic metal and the reactive gas may be merged at the merge position A. The organic metal and the reactive gas contained in the mixed gas are preferably supplied separately up to the merge position A. This makes it possible to prevent the organic metal and the reactive gas from reacting with each other before they are merged. When doping silicon or the like, the organic metal and the dopant gas may be mixed in advance and supplied to the merge position A.

[0028] In the process of supplying an organic metal to vapor phase growth apparatus 100 to form a compound semiconductor film on substrate 2 (film formation process), deposits 24 containing carbon may adhere to the inner walls of the flow channel. Cleaning is required to remove deposits 24 from the flow channel.

[0029] To clean the vapor deposition apparatus 100, oxygen (O ２ ) gas is flowed to clean deposits 24 adhering to the inner walls of the flow channels. Carbon contained in the deposits 24 reacts with oxygen to form gases such as carbon monoxide and carbon dioxide, which are then removed from the inner walls of the flow channels. The illustrated example shows deposits 24 accumulated in the upstream flow channel 20 and the intermediate flow channel 26. Although not specifically shown, if deposits 24 are accumulated on the inner walls of the downstream flow channel 29, the deposits 24 are similarly removed by flowing oxygen gas.

[0030] There are no particular limitations on the number, structure, shape, etc. of channels formed in upstream flow channel 20 of vapor phase growth apparatus 100. For example, when upstream flow channel 20 is partitioned into top channel 21, middle channel 22, and bottom channel 23, the following cleaning method can be used.

[0031] (1) A cleaning method in which oxygen gas is flowed from each of the top channel 21, the middle channel 22, and the bottom channel 23. (2) A cleaning method in which oxygen gas is flowed from the middle channel 22, and an inert gas is flowed from the top channel 21 and the bottom channel 23. (3) A cleaning method in which oxygen gas is flowed from the top channel 21 and the bottom channel 23, and a mixed gas of oxygen gas and an inert gas is flowed from the middle channel 22. (4) A cleaning method in which an inert gas is flowed from the top channel 21 and the bottom channel 23, and a mixed gas of oxygen gas and an inert gas is flowed from the middle channel 22. (5) A cleaning method in which a mixed gas of oxygen gas and an inert gas is flowed from each of the top channel 21, the middle channel 22, and the bottom channel 23.

[0032] In the upstream flow channel 20, which is divided into multiple channels, oxygen gas or a mixed gas containing oxygen gas may be flowed through all of the channels. When oxygen gas or a mixed gas containing oxygen gas is flowed through some of the multiple channels, an inert gas may be flowed through the other channels. The mixed gas is preferably a mixed gas of oxygen gas and an inert gas, and is preferably a mixed gas that does not contain an organic metal or a halogen-based gas such as chlorine.

[0033] Examples of the inert gas flowing alone or in a mixed gas through the channels during cleaning include argon gas, helium gas, etc. The composition of the gas flowing may be changed depending on the amount of deposits 24 in each channel. The gas flowing through each channel may be a mixed gas with an appropriately changed gas composition ratio, oxygen gas alone, an inert gas alone, or the like.

[0034] During cleaning, the flow rate of the oxygen gas or the mixed gas containing oxygen gas is not particularly limited, and can be set appropriately depending on the cross-sectional area of ​​the upstream flow channel 20, the amount of deposits 24, etc. In addition to the flow rate necessary to remove the deposits 24, the gas flow rate may also include a flow rate for preventing backflow of the gas, a flow rate for preventing the deposits 24 removed from the inner wall from adhering again to the inner wall from the gas phase, etc.

[0035] During cleaning, when oxygen gas or a mixed gas containing oxygen gas is flowed through the upstream flow channel 20, the reaction tube 1 may be heated using the electric furnace 10. The heating temperature when heating the reaction tube 1 is not particularly limited, but examples thereof include 800 to 1200°C. The temperature at which carbon in the deposits easily reacts with oxygen in the gas phase is 800°C or higher. The upper limit of the temperature is not particularly limited, but can be set taking into consideration factors such as saving the energy required to maintain a high temperature and the heat resistance of the reaction tube 1 and other devices. For example, when the reaction tube or flow channel is made of quartz glass, devitrification can be prevented at temperatures of 1200°C or lower.

[0036] When cleaning the deposits 24, the electric furnace 10 preferably focuses on heating the area where the deposits 24 may adhere. For example, it is preferable to heat a heating area H extending from near the upstream end of the electric furnace 10 to near the upstream end of the substrate 2 in the gas flow direction (the left-right direction in the figure).

[0037] The electric furnace 10 may be heated so that when a compound semiconductor film is grown on the substrate 2 (during film formation), the temperature at the position where the substrate 2 is placed is higher than the temperature at the joining position A. The electric furnace 10 may also be heated so that when the deposit 24 is cleaned (during cleaning), the temperature at the joining position A is higher than the temperature at the position where the substrate 2 is placed. Note that, although the organic metal and the reactive gas may be joined at the joining position A during film formation, it is not necessary to join the organic metal and the reactive gas at the joining position A during cleaning.

[0038] To change the temperature inside the reaction tube 1 during film formation and cleaning, for example, the electric furnace 10 may be divided into multiple zones and the output ratio of each zone may be adjusted. As described above, the electric furnace 10 in the illustrated example includes the upstream heater 11, the intermediate heater 12, and the downstream heater 13, and the temperatures in these three zones can be set individually.

[0039] Furthermore, even if the electric furnace 10 is not divided into multiple zones, the temperature inside the reaction tube 1 during film formation and cleaning may be changed by adjusting the position of the electric furnace 10. For example, during film formation, the electric furnace 10 may be positioned so that the center of the region heated by the electric furnace 10 approaches the substrate 2 in the gas flow direction. Furthermore, during cleaning, the electric furnace 10 may be positioned so that the center of the region heated by the electric furnace 10 approaches the confluence position A in the gas flow direction.

[0040] During cleaning, it is preferable not to supply source gas such as organic metals from the source gas flow path to the flow channel. If the deposit 24 contains organic metals, the organic metals may be re-released during cleaning. In this case, temperature conditions may be selected that decompose the organic metals. If the deposit 24 does not contain organic metals, temperature conditions may be selected that oxidize and remove carbon.

[0041] The cleaning step may be performed before or after the film formation step. When the reaction tube 1 is heated in the cleaning step, the reaction tube 1 may be continuously heated between the film formation step and the cleaning step, or a cooling step in which the reaction tube 1 is cooled may be performed between the film formation step and the cleaning step.

[0042] The frequency of the cleaning process relative to the film formation process is not particularly limited and can be set appropriately depending on the situation. Since there is no need to remove the flow channel during cleaning, the frequency of cleaning may be increased compared to wet cleaning. For example, the cleaning process may be performed every time the film formation process is performed. Furthermore, the cleaning process may be performed every time the film formation process is performed multiple times.

[0043] The vapor phase growth apparatus 100 having the function of cleaning the deposits 24 may have an operation mode for carrying out a cleaning process separate from an operation mode for carrying out a film formation process. The vapor phase growth apparatus 100 may also have a control means for carrying out the cleaning process separate from the film formation process. Examples of the control means include a computer, a controller, etc. The control means may also have a program or the like for carrying out the cleaning process separate from the film formation process.

[0044] The vapor phase growth apparatus 100 may have a function of automatically performing the cleaning step. The vapor phase growth apparatus 100 may have a function of stopping the supply of source gases during the cleaning step. In this case, the vapor phase growth apparatus 100 may be configured to be able to supply a gas supply source used as a reactant gas or a carrier gas in the film formation step to the flow channel in the cleaning step.

[0045] In the cleaning step, the substrate 2 may be held by a substrate holding jig such as a hanging substrate holder 3 in order to block the opening of the flow channel. The substrate used in the cleaning step may be the same type as the substrate 2 used in the film formation step, or a different type of substrate. The vapor phase growth apparatus 100 may have a function of discarding the substrate 2 used in the cleaning step so that it will not be used in the film formation step.

[0046] The substrate 2 used in the film formation step is not particularly limited as long as it is plate-shaped and can support a compound semiconductor film, and may be any known substrate. Examples of the substrate include an insulating substrate, a conductive substrate, and a semiconductor substrate. In this embodiment, the substrate 2 is preferably a crystalline substrate. The compound semiconductor film formed on the substrate 2 is preferably an epitaxial film.

[0047] The crystalline substrate is not particularly limited as long as it is a substrate containing a crystalline material as a main component, and examples thereof include an insulating substrate, a conductive substrate, a semiconductor substrate, a single crystal substrate, and a polycrystalline substrate. Examples of the crystalline substrate include a substrate containing a crystalline material having a corundum structure as a main component, a substrate containing a crystalline material having a β-gallia structure as a main component, and a substrate having a hexagonal crystal structure. The term "main component" refers to a substrate containing 50% or more of the crystalline material, preferably 70% or more, and more preferably 90% or more, of the crystalline material in terms of composition ratio in the substrate.

[0048] Examples of substrates containing a crystalline substance having a corundum structure as a main component include a sapphire substrate and an α-type gallium oxide substrate. Examples of substrates containing a crystalline substance having a β-gallium structure as a main component include a β-Ga ２ O ３ Substrate, or β-Ga ２ O ３ and Al ２ O ３ Examples of the substrate having a hexagonal crystal structure include a SiC substrate, a ZnO substrate, and a GaN substrate. Examples of other crystal substrates include a Si substrate. The thickness of the crystal substrate is not particularly limited, but is preferably 50 to 2000 μm, and more preferably 200 to 800 μm.

[0049] The compound semiconductor film that can be formed by the vapor phase growth apparatus of this embodiment is particularly suitable for use in semiconductor devices, and is particularly useful for power devices. Examples of semiconductor devices formed using the compound semiconductor film include transistors such as MIS and HEMT, TFTs, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements.

[0050] The compound semiconductor film of this embodiment may be used in a semiconductor device or the like in the state in which it is formed on a substrate, or may be peeled off from the substrate or the like by a known means and then applied to a semiconductor device or the like. The semiconductor device may be further used by a known means as a power module, an inverter, or a converter, and further may be used in a semiconductor system or the like using, for example, a power supply device.

[0051] A: Confluence position G1: First source gas G2: Second source gas H: Heating region 1: Reaction tube 2: Substrate 3: Hanging substrate holder 10: Electric furnace 11: Upstream heater 12: Intermediate heater 13: Downstream heater 20: Upstream flow channel 21: Top channel 22: Middle channel 23: Bottom channel 24: Deposit 26: Intermediate flow channel 27: Top opening 29: Downstream flow channel 31: First source gas supply pipe 32a, 32b: Second source gas supply pipe 100: Vapor phase growth apparatus

Claims

1. A method for cleaning deposits in a vapor phase growth apparatus that uses an electric furnace to heat a reaction tube, comprising flowing oxygen gas through a flow channel disposed within the reaction tube to clean carbon-containing deposits adhering to the inner wall of the flow channel.

2. A vapor phase growth apparatus using an electric furnace to heat a reaction tube, the vapor phase growth apparatus having the functions of growing a compound semiconductor film on a substrate by flowing an organic metal and a reaction gas through a flow channel disposed within the reaction tube, and cleaning carbon-containing deposits adhering to the inner wall of the flow channel by flowing oxygen gas through the flow channel.

3. The vapor phase growth apparatus according to claim 2, wherein the electric furnace heats the substrate so that the temperature at the position where the substrate is placed is higher than the temperature at the confluence of the organic metal and the reactive gas when growing the compound semiconductor film on the substrate, and the electric furnace heats the substrate so that the temperature at the confluence is higher than the temperature at the position where the substrate is placed when cleaning the carbon-containing deposits.

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